Need to unscrew a screw? Can't see what it looks like and don't know the type? Redditor spacewolf46 suggests pushing your finger into the screw for a few seconds to find out:

When you need to unscrew something in a hard to reach place and can't get a good look at the screw type, push your finger on the head for a few seconds, then look at your fingertip.

As you can see from the photo above, the impression left from the screw will tell you what kind of screwdriver you need. Of course, you could grab a ladder and a flashlight and use your eyes to find out, but this method is faster and kind of fun.